1. Field of the Invention
The invention relates to testing materials for possible use during the molding of optical lenses. The invention also relates to molding optical lenses, particularly ophthalmic lenses, from polymerizable compositions.
2. Description of Related Art
The traditional mold comprises a molding cavity defined by two mold pieces, each typically made of mineral glasses, and an annular closure member, such as a gasket or an adhesive tape, disposed around the periphery of the two mold pieces and attached to them. The conventional way to fill such a two-piece mold is by causing the molding material to flow into the molding cavity through a casting opening provided for this purpose in the closure member. In at least a partly automated process, the molding cavity to be filled is vertically aligned with a filling device that is adapted to deliver a particular quantity of molding material through a nozzle.
One way to fill such a vertically oriented mold is by filling the molding cavity through a nozzle disposed at the top of the mold periphery, which nozzle introduces molding material into the molding cavity by gravity only. See, for example, U.S. Pat. No. 5,110,514. Experience has shown that in the case of a relatively long waiting time (for example, on the order of two hours) between filling the mold and starting polymerization, unless special measures are implemented, the optical lenses obtained frequently have localized optical defects of greater or lesser severity, which leads to relatively high reject rates.
To overcome such problems, U.S. Pat. Nos. 5,547,618 and 5,662,839 propose filling the molding cavity of a vertically oriented two-piece mold through a casting opening formed in a lower part of the closure member and using a pumping mechanism adapted to cause the molding material to flow without significantly pressurizing it. Typically, filling of the molding cavity in this manner is effected using a pipe connected to a pressurized molding material reservoir and applied, like a filling nozzle, to the casting opening. With such a method, it is possible to start polymerization immediately after filling. However, in the case of molding material that reacts at room temperature in less than ten minutes, such as the formulations disclosed in U.S. Pat. No. 5,973,098, the pipe will quickly clog.
One solution to this problem involves the use of a check valve provided in the closure member as disclosed in U.S. patent application Ser. No. 09/814,318, the inventors of which are Gabriel Keita and Yassin Yusef Turshani. While use of a check valve, which may be a duck bill valve as disclosed in the referenced application, addresses the aforementioned clogging problem, use of such valves may be expensive.
Another way of filling a vertically oriented mold is disclosed in Japanese Patent Application No. 8-308223 (Unexamined Japanese Patent 10-146846). The Japanese application discloses molding cavity A defined by two molding pieces 1 and annular closure member comprising adhesive tape 2. An elastic body with a rubber-like elasticity 3 is attached to the adhesive tape at the top of the vertically oriented mold. As an alternative to the elastic body 3, the Japanese application also discloses a coating 4 that has a rubber-like elasticity. The Japanese application discloses introducing molding material into the cavity A through an injection needle placed through both the elastic body 3 or coating 4 and the adhesive tape 2 while using an exhaust tube placed into the molding cavity A through another opening in the elastic body 3 or coating 4 and the adhesive tape 2. The Japanese application discloses withdrawing the nozzle and the exhaust tube after filling the cavity A with the molding material. The Japanese application notes that two holes formed by the introduction of the nozzle (an example of which is an injection needle) and the exhaust tube are closed after those items are removed by virtue of the rubber-like elasticity of elastic body 3 or coating 4. Next, the molding material is cured in a heating furnace for about 10 to 15 hours at about 100° C. The filling method disclosed in the Japanese application is not confronted with, and therefore does not address, the problem of molding material leaking out of the molding cavity A around the injection needle or exhaust tube. This follows because those two instruments enter cavity A from the top of the vertically oriented mold. In addition, problems with encountering localized optical defects due, for example, to microbubbles that form in the molding material as it fills up cavity A may be present with the method disclosed in the Japanese application unless special measures are implemented.